Semiconductor devices and method of manufacturing them

ABSTRACT

With conventional device, the quantity of complex defects differs with each semiconductor device because the concentration of impurities intrinsically contained differs for each silicon wafer. Consequently, there is an undesirable variation in characteristics among the semiconductor devices. The invention provides a method for manufacturing PIN type diode which comprises an intermediate semiconductor region in which complex defects are formed. The method comprises introducing impurities (for example, carbon), which are the same kind of impurities intrinsically contained in the intermediate semiconductor region, into the intermediate semiconductor region, and irradiating the intermediate semiconductor region with helium ions to form point defects.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 11/436,616, filed May 19,2006 which is incorporated herein by reference.

The present application claims priority based on Japanese PatentApplication 2005-147911 filed on May 20, 2005 and Japanese PatentApplication 2006-138606 filed on May 18, 2006 the contents of which arehereby incorporated by reference within this application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a semiconductor device comprising asemiconductor region having complex defects. Further, the presentinvention relates to a method of manufacturing the semiconductor devicecomprising the semiconductor region having complex defects.

In order to improve characteristics (typically the switchingcharacteristics) of a semiconductor device, complex defects are formedin a semiconductor region of the semiconductor device. The complexdefect is a defect where a point defect in the semiconductor region andan impurity atom are combined. The term impurity or impurities in thisspecification do not refer to conductive impurities or doses that areintentionally introduced to the semiconductor region to determineconductivity of the semiconductor region, but refer to non-conductiveimpurities intrinsically contained in the semiconductor region. Forexample, elements of non-conductive impurities include oxygen, carbon,nitrogen, etc. Further, the term point defect refers to a localdisturbance of a crystal lattice forming the semiconductor region. Thepoint defect includes a vacancy type and an interstitial atom type.Complex defect in which the point defect and the impurity are combinedis known to exist stably within the semiconductor region.

Complex defects form a deep energy level, and, for this reason, complexdefects can provide locations where positive holes and electronsrecombine. Therefore, by forming complex defects in the semiconductorregion, it becomes possible to control the lifetime of carriers. As aresult, the semiconductor device can be formed with less loss of energy,less recovery surge voltage, etc. This type of semiconductor device istaught in Japanese Patent Application Publication No. 1995-106605.

A method of forming complex defects in PIN type diode 200 will bedescribed with reference to FIG. 11. PIN type diode 200 comprises n⁺type cathode semiconductor region 222, n⁻ type (or i type) intermediatesemiconductor region 224, and p⁺ type anode semiconductor region 226.PIN type diode 200 is made of silicon wafers. Cathode semiconductorregion 222 is formed by introducing n type impurities into a bottomsurface of an n⁻ type silicon wafer. Anode semiconductor region 226 isformed by introducing p type impurities into a top surface of the n⁻type silicon wafer. An anode electrode 232 is connected to anodesemiconductor region 226. The configuration shown in FIG. 11 is acondition prior to a cathode electrode being formed.

Electron beam irradiation is usually used to form complex defects. Asshown in FIG. 11, in the case where complex defects are formed inintermediate semiconductor region 224, the electron beams are irradiatedfrom cathode semiconductor region 222 side towards a predetermined depthof intermediate semiconductor region 224. Point defects 244 are formedin intermediate semiconductor region 224 which has been irradiated bythe electron beams. Complex defects are formed by combining pointdefects 244 with the impurities that intrinsically exist in the vicinityof point defects 244 thus formed.

SUMMARY OF THE INVENTION

As described above, when manufacturing PIN type diode 200, siliconwafers are usually used. The concentration of the impuritiesintrinsically contained in silicon wafers often differs greatly witheach silicon wafer. Generally, silicon wafers are obtained by slicing awafer off an ingot. In most cases, the concentration of impuritiescontained in a silicon wafer obtained by slicing off an upper part of aningot differs greatly from the concentration of impurities contained ina silicon wafer obtained by slicing off a lower part of the ingot. Asdescribed above, complex defects are formed by combining point defectswith impurities. As a result, the quantity of complex defects formed isdetermined based on which contributes a lower quantity to the combiningprocess: the quantity of impurities intrinsically contained in thesemiconductor region, or the quantity of point defects formed fromirradiation of electron beams.

FIG. 12 shows the distribution of impurity concentration along the depthdirection of the intermediate semiconductor region 224. The impurityconcentration of intermediate semiconductor region 224 obtained fromseparate silicon wafers is shown by 212 a and 214 a in the figure. Asshown in FIG. 12, the impurity concentration that is intrinsicallycontained differs for each of the silicon wafers. The quantity of pointdefects 244 that are formed by electron beam irradiation can be adjustedby adjusting the output of the electron beam irradiation. If thequantity of point defects 244 is adjusted to be lower than a lowerimpurity concentration (212 a in the figure), the quantity of complexdefects formed in a intermediate semiconductor region containing thelower impurity concentration (212 a in the figure) and the quantity of aintermediate semiconductor region containing the higher impurityconcentration (214 a in the figure) become approximately equal. However,if the quantity of point defects 244 is adjusted to be higher than thelower impurity concentration (212 a in the figure), the quantity ofcomplex defects formed in the semiconductor region containing the lowerimpurity concentration (212 a) will be lower than the quantity ofcomplex defects formed in the semiconductor region containing the higherimpurity concentration (214 a).

In general, the impurity concentration of the silicon wafer is notmeasured during the process of forming the complex defects. Instead,point defects 244 are formed so as to have a larger concentration thanthe higher impurity concentration (214 a) intrinsically contained in thesilicon wafer.

In this case, as shown in FIG. 13, when a sufficient quantity of pointdefects 244 is formed, the quantity of complex defects formed within thesemiconductor region will be determined by impurity concentration 212 aor 214 a intrinsically contained in the silicon wafers. Therefore, whenimpurity concentrations 212 a and 214 a intrinsically contained in thesilicon wafers differ, the quantity of complex defects formed in thesilicon wafers also differ. As a result, the characteristics of thesemiconductor devices obtained from differing silicon wafers varydepending on the silicon wafer from which the semiconductor device isformed.

The present invention was created to solve the aforementioned problem.In the above example, PIN type diode 200 was used to explain theproblem. However, the same type of problem can also occur with othertypes of semiconductor devices. Further, complex defects are formed insemiconductor devices not only to improve switching characteristics, butalso to improve other characteristics such as on-resistance, voltagewithstanding characteristics, quantity withstanding characteristics,etc. The techniques taught in the present specification are useful in avariety of purposes for forming complex defects in a semiconductorregion of a semiconductor device. Further, in the above example, siliconwafers were used to explain the problem. However, the same problemexists with semiconductor wafers made from other materials because theimpurity concentration is different for each wafer. Therefore, thetechniques taught in the present specification are also useful in caseswhere semiconductor wafers other than silicon are utilized.

One object of the present invention is to reduce the variation inquantity of complex defects formed in semiconductor regions.

Another object of the present invention is to reduce the variation incharacteristics of the semiconductor devices.

Another object of the present invention is to present a method formanufacturing the above semiconductor devices.

Another object of the present invention is to present a semiconductordevice comprising a semiconductor region that has been adjusted to havea desired quantity of complex defects.

The present invention is characterized in that the impurityconcentration within a semiconductor region, which is originallydifferent for each semiconductor wafer, is uniformized by means of theprocess disclosed below. Usually, the impurity concentrationintrinsically contained within the semiconductor region is extremelylow. As a result, even a slight difference in the impurity concentrationamong the semiconductor wafers can be considered significant because theoverall concentration of the impurities is low. However, the differencein the impurity concentration among the semiconductor wafers becomesnegligible when the overall concentration of the impurities becomeshigh. The present invention was created with this point in mind. In thepresent invention, variations in impurity concentration among differingwafers are made negligible by introducing a large quantity of impuritiesof the same kind as the impurities intrinsically contained within thesemiconductor region. By utilizing the present invention, the variationof impurity concentrations among differing wafers becomes negligible.

The present invention teaches a method of manufacturing a semiconductordevice comprising a semiconductor region having complex defects. Themethod comprises a step of introducing impurities into the semiconductorregion. The introducing impurities are of the same kind as impuritiesintrinsically contained within the semiconductor region. The methodfurther comprises a step of forming point defects in the semiconductorregion. The sequence of the above steps is not significant. Depending onthe situation, the above steps can be implemented simultaneously.

In order to better understand the techniques of the present invention,an outline of the techniques will be described metaphorically, thoughthis is not very precise. The concentration of impurities intrinsicallycontained in the semiconductor region of semiconductor wafer “A” shallbe 1.0, and the concentration of impurities contained in thesemiconductor region of semiconductor wafer “B” shall be 2.0. In thiscase, the difference between the concentrations of impuritiesintrinsically contained in the two semiconductor regions is such thatthe concentration of one is twice the concentration of the other. If100.0 impurities of the same kind as the impurities intrinsicallycontained in the semiconductor regions are introduced into bothsemiconductor regions, the impurity concentration of the semiconductorregion of the semiconductor wafer “A” becomes 101.0, and the impurityconcentration of the semiconductor region of the semiconductor wafer “B”becomes 102.0. By introducing a large quantity of impurities, thevariation in the impurity concentrations of the two semiconductorregions becomes relatively small. It is consequently possible, byadjusting the quantity of point defects that is formed, to reduce thevariation in the quantity of complex defects formed in the twosemiconductor regions. Further, in a case where more complex defectsthan required have been formed by introducing a large quantity ofimpurities, a process may be performed to remove the complex defects.This process may be performed after the large quantity of complexdefects has been formed. It is possible to adjust the quantity ofcomplex defects to the required quantity while reducing the variation inthe quantity of complex defects formed among the semiconductor regions.

In the method according to the present invention, it is preferred thatthe semiconductor region is exposed to a light ion beam and/or anelectron beam in order to form point defects.

If a light ion beam and/or an electron beam is utilized, it becomeseasier to form the point defects in local regions of the semiconductorregion.

In the method according to the present invention, it is preferred that aregion where the largest quantity of the impurities is introduced and aregion where the largest quantity of the point defects is formed arelocated at approximately the same depth in the semiconductor region.

If the above method is utilized, complex defects can be formed at localregions of the semiconductor region. With the above method, thecharacteristics of the semiconductor device can be markedly improved.

In the method according to the present invention, it is preferred thatthe highest concentration of the impurities introduced into thesemiconductor region is greater than the concentration of the impuritiesintrinsically contained within the semiconductor region.

If the above method is utilized, the quantity of impuritiesintrinsically contained within local regions of the semiconductor regionwill be increased twice as much, or more, by means of introducingimpurities. When the quantity of impurities is increased twice as muchor more as the quantity of impurities intrinsically contained, thevariation of the impurity concentrations of the semiconductor devicesbecomes negligible.

In the method according to the present invention, the step ofintroducing impurities may be performed prior to the step of formingpoint defects. In other words, the step of introducing impurities andthe step of forming point defects are separate steps, and the former maybe performed before the latter.

In the method according to the present invention, the method may furthercomprise heating the semiconductor region to more than 800 degreesCelsius between the step of introducing impurities and the step offorming point defects.

By heating the semiconductor region to more than 800 degrees Celsiusafter the step of introducing impurities, the damage incurred by thesemiconductor region when the impurities were introduced can berecovered. Further, by heating the semiconductor region to more than 800degrees Celsius after the step of introducing impurities, the introducedimpurities can be displaced in the lattice location of the semiconductorregion. By utilizing the aforementioned method, impurities can beintroduced into the semiconductor region in large quantities.

In the method according to the present invention, it is preferred thatthe method further comprise heating the semiconductor region to between200 degrees Celsius and 600 degrees Celsius after the step of formingpoint defects.

The combining of the impurities and the point defects can be acceleratedby heating the semiconductor region to between 200 degrees Celsius and600 degrees Celsius. Further, the quantity of complex defects falls ifthe semiconductor region is heated to more than 600 degrees Celsius.However, as stated above, it may be desirable to reduce the quantity ofcomplex defects when required. In this case, the complex defects mayfirst be formed by heating the semiconductor region to between 200degrees Celsius and 600 degrees Celsius, and then the semiconductorregion may be heated to more than 600 degrees Celsius to reduce thequantity of complex defects.

In the method according to the present inventions it is preferred thatthe impurities being non-conductive type are introduced into thesemiconductor region. Non-conductive type impurities are different fromimpurities or doses that function as acceptors or donors within thesemiconductor region. Further, the kind of non-conductive typeimpurities differs depending on the material of the semiconductorregion.

In the method according to the present invention, silicon may be used asthe semiconductor material of the semiconductor region. In this case,impurities selected from at least one of carbon, oxygen, nitrogen,fluorine, argon, silicon, or germanium are introduced into thesemiconductor region.

In the method of the present invention, the aforementioned elements maybe utilized in combination. Further, by selecting the appropriateelements to use, the required types of complex defects can be formedaccordingly.

In the case where the semiconductor material is silicon, carbon andoxygen, for example, are used for forming complex defects that trappositive holes. Oxygen and nitrogen are used for forming complex defectsthat trap electrons. In this way, the required types of complex defectscan be formed by selecting the appropriate elements from theaforementioned elements.

A semiconductor device according to the present invention comprises asemiconductor region having complex defects. With the semiconductordevice according to the present invention, the impurities contained inthe semiconductor region have an uneven concentration distribution alonga depth direction of the semiconductor region.

The uneven concentration distribution along the depth direction of thesemiconductor region indicates that impurities have been introducedintentionally into the semiconductor region. If semiconductor deviceshave the above characteristic, it is clear that those semiconductordevices utilize the technical concepts of the present invention.

In the semiconductor device according to the present invention, it ispreferred that the impurities being the non-conductive type have anuneven concentration distribution along the depth direction of thesemiconductor region.

In the semiconductor device according to the present invention, it ispreferred that the impurities have a maximum concentration of greaterthan or equal to twice the minimum concentration along the depthdirection of the semiconductor region.

The minimum concentration is approximately equal to the concentration ofimpurities that is intrinsically contained in the semiconductor region.That the impurities are distributed in such a way indicates thatimpurities have been introduced intentionally into the semiconductorregion, giving the semiconductor region a higher concentration ofimpurities than the concentration of impurities intrinsically containedtherein. If semiconductor devices have the above characteristic, it isclear that those semiconductor devices utilize the technical concepts ofthe present invention.

The present invention can be realized in a diode semiconductor device.The semiconductor of the present invention comprises an anodesemiconductor region that includes impurities of a first conductivity, acathode semiconductor region that includes a high concentration ofimpurities of a second conductivity type, and an intermediatesemiconductor region that includes a low concentration of impurities ofthe second conductivity type or includes substantially no impurities.Further, the intermediate semiconductor region is formed between theanode semiconductor region and the cathode semiconductor region. Withthe semiconductor device of the present invention, non-conductiveimpurities have an uneven concentration distribution along the directionthat joins the anode semiconductor region and the cathode semiconductorregion.

That the non-conductive impurities are distributed unevenly indicatesthat the non-conductive impurities have been introduced intentionallyinto the semiconductor device. It is clear that the technical conceptsof the present invention are utilized with semiconductor devices havingthe above characteristic.

With respect to the diode semiconductor device, the anode semiconductorregion may shares a boundary with the intermediate semiconductor region.In this case, it is preferred that the position of the maximumconcentration of the non-conductive impurities is located in thevicinity of the boundary between the anode semiconductor region and theintermediate semiconductor region.

The reverse-recovery characteristics of the semiconductor device areimproved if complex defects are formed locally in the vicinity of theboundary between the anode semiconductor region and the intermediatesemiconductor region.

With respect to this diode semiconductor device, it is preferred thatthe non-conductive impurities have a maximum concentration that isgreater than or equal to twice the minimum concentration along thedirection that joins the anode semiconductor region and the cathodesemiconductor region.

That the non-conductive impurities are distributed in such a wayindicates that the non-conductive impurities have been introducedintentionally into the semiconductor device. It is clear that thetechnical concepts of the present invention are utilized withsemiconductor devices having the above characteristic.

The present invention can be realized as an IGBT (Insulated Gate BipolarTransistor) semiconductor device. Such a semiconductor device of thepresent invention comprises a collector electrode. The semiconductordevice further comprises a collector semiconductor region that includesimpurities of a first conductivity type. The collector semiconductorregion is formed above the collector electrode. The semiconductor devicefurther comprises a second conductivity type base semiconductor regionthat includes impurities of the second conductivity type. The secondconductivity type base semiconductor region is formed above thecollector semiconductor region. The semiconductor device furthercomprises a first conductivity type base semiconductor region thatincludes impurities of the first conductivity type. The firstconductivity type base semiconductor region is separated from thecollector semiconductor region by the second conductivity type basesemiconductor region. The semiconductor device further comprises anemitter semiconductor region that includes impurities of the secondconductivity type. The matter semiconductor region is separated from thesecond conductivity type base semiconductor region by the firstconductivity type base semiconductor region. The semiconductor devicefurther comprises a gate electrode that faces, via an insulating film,the first conductivity type base semiconductor region that separates theemitter semiconductor region and the second conductivity type basesemiconductor region. With respect to the semiconductor device of thepresent invention, non-conductive impurities have an unevenconcentration distribution along the direction that joins the collectorsemiconductor region and the emitter semiconductor region.

That the non-conductive impurities are distributed unevenly indicatesthat the non-conductive impurities have been introduced intentionallyinto the semiconductor device. It is clear that the technical conceptsof the present invention are utilized with semiconductor devices havingthe above characteristic.

The aforementioned IGBT semiconductor device may be configured as anon-punch-through IGBT semiconductor device, where the collectorsemiconductor region shares a boundary with the second conductivity typebase semiconductor region. This non-punch-through IGBT semiconductordevice can apply to bulk type IGBT. With respect to thisnon-punch-through IGBT semiconductor device, it is preferred that theposition of maximum concentration of non-conductive impurities islocated in the vicinity of the boundary between the collectorsemiconductor region and the second conductivity type base semiconductorregion.

The reverse-recovery characteristics of the semiconductor device areimproved if complex defects are formed in the vicinity of the boundarybetween the collector semiconductor region and the second conductivitytype base semiconductor region.

The aforementioned IGBT semiconductor device may further comprise abuffer semiconductor region that includes a higher concentration ofimpurities of the second conductivity type than the second conductivitytype base semiconductor region The buffer semiconductor region is formedbetween the collector semiconductor region and the second conductivitytype base semiconductor region. This IGBT semiconductor device isconfigured as a punch-through IGBT semiconductor device.

With respect to the punch-through IGBT semiconductor device, thecollector semiconductor region may shares a boundary with the buffersemiconductor region. Further, with this type of semiconductor device,it is preferred that the position of maximum concentration ofnon-conductive impurities is located in the vicinity of the boundarybetween the collector semiconductor region and the buffer semiconductorregion.

The reverse-recovery characteristics of the semiconductor device areimproved if complex defects are formed in the vicinity of the boundarybetween the collector semiconductor region and the buffer semiconductorregion.

With respect to the aforementioned IGBT semiconductor device, thecollector semiconductor region may be formed as a plurality of collectorsemiconductor regions, dispersed between the collector electrode and thesecond conductivity type base semiconductor region. With this type ofsemiconductor device, the collector electrode and the secondconductivity type base semiconductor region are electrically connectedvia the open space between the collector semiconductor regions. ThisIGBT semiconductor device is configured as a collector-short IGBTsemiconductor device.

With respect to the collector-short IGBT semiconductor device, thecollector semiconductor region may shares a boundary with the secondconductivity type base semiconductor region. Further, with this type ofsemiconductor device, it is preferred that the position of maximumconcentration of non-conductive impurities is located in the vicinity ofthe boundary between the collector semiconductor region and the secondconductivity type base semiconductor region.

The reverse-recovery characteristics of the semiconductor device areimproved if complex defects are formed in the vicinity of the boundarybetween the collector semiconductor region and the second conductivitytype base semiconductor region.

With respect to the aforementioned IGBT semiconductor device, it ispreferred that the non-conductive impurities have a maximumconcentration that is greater than or equal to twice the minimumconcentration along the direction that joins the collector semiconductorregion and the emitter semiconductor region

That the non-conductive impurities are distributed in such a wayindicates that the non-conductive impurities have been introducedintentionally into the semiconductor device. It is clear that thetechnical concepts of the present invention are utilized withsemiconductor devices having the above characteristic.

By introducing a large quantity of impurities into a semiconductorregion, the variation in the impurities intrinsically contained insemiconductor devices becomes negligible. As a result, the variation ofcomplex defects that are formed also becomes negligible, and asemiconductor device with predetermined characteristics can be stablyobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of essential portions of asemiconductor layer provided with a PIN type diode of the presentembodiment.

FIG. 2 shows a process of injecting carbon ions into an intermediatesemiconductor region.

FIG. 3 shows a process of irradiating the intermediate semiconductorregion with helium ions.

FIG. 4 shows a process of forming complex defects in the intermediatesemiconductor region.

FIG. 5 shows the distribution of impurity concentrations intrinsicallycontained within the intermediate semiconductor region of the presentembodiment.

FIG. 6 shows the distribution of the impurity concentrations in theintermediate semiconductor region after carbon ions have been injected.

FIG. 7 shows the distribution of the complex defects in the intermediatesemiconductor regions of the present embodiment.

FIG. 8(A) shows a simplified cross-sectional diagram of a essentialparts of a semiconductor device according to the second embodiment.

FIG. 8(B) shows the concentration distribution of carbon and complexdefects.

FIG. 9(A) shows a simplified cross-sectional diagram of a essentialparts of a semiconductor device according to the third embodiment.

FIG. 9(B) shows the concentration distribution of oxygen and complexdefects.

FIG. 10(A) shows a simplified cross-sectional diagram of a essentialparts of a semiconductor device according to the fourth embodiment.

FIG. 10(B) shows the concentration distribution of nitrogen and complexdefects.

FIG. 11 shows a conventional process of forming complex defects.

FIG. 12 shows the distribution of impurity concentrations intrinsicallycontained within a conventional intermediate semiconductor region.

FIG. 13 shows the distribution of complex defects in a conventionalintermediate semiconductor region.

DETAILED DESCRIPTION OF THE INVENTION Description of the PreferredFeatures

The features of the present invention will be described below.

(First Feature)

Silicon, gallium arsenide, silicon carbide, cadmium, germanium, galliumnitride, etc. may be utilized as the semiconductor material of thesemiconductor region. If silicon material is utilized, then carbon,oxygen, nitrogen, fluorine, argon, silicon, or germanium is used as theimpurity. If gallium arsenide material is utilized, then silicon,oxygen, carbon, or nitrogen is used as the impurity. If silicon carbideis utilized, then oxygen or nitrogen is used as the impurity. If cadmiumis utilized, then the carbon, oxygen, or nitrogen is used as theimpurity. If germanium is utilized, then carbon, oxygen, or nitrogen isused as the impurity. If gallium nitride is utilized, then carbon oroxygen is used as the impurity.

(Second Feature)

The maximum concentration of impurities introduced in the step ofintroducing impurities and the depth of these impurities are determinedby a dose quantity (Dose1) and the half width of the injected energy(FWHM1), and the maximum concentration of impurities is represented asDose1/FWHM1. It is preferred that this maximum impurity concentration(Dose1/FWHM1) is greater than the impurity concentration intrinsicallycontained in the semiconductor region (ND). That is, it is preferredthat a relationship is realized wherein ND<Dose1/FWHM1.

(Third Feature)

Hydrogen, heavy hydrogen, helium-3 and/or helium-4 can be utilized asthe light ions that are irradiated when point defects are formed. Themaximum concentration of light ions that are introduced into thesemiconductor region is determined by a dose quantity (Dose2) and thehalf width of the injected energy (FWHM2), and is represented asDose2/FWHM2. It is preferred that this maximum introduced concentration(Dose2/FWHM2) is greater than the sum of the impurity concentrationintrinsically contained in the semiconductor region (ND) and the maximumimpurity concentration (Dose1/FWHM1). That is, it is preferred that arelationship is realized wherein ND+Dose1/FWMHM1<Dose2/FWHM2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method of forming complex defects in PIN type diode 10 will bedescribed with reference to FIGS. 1 to 7. FIGS. 1 to 4 showcross-sectional views of essential parts of the PIN type diode 10. FIGS.1 to 4 also show manufacturing flows of the PIN type diode 10. FIGS. 5and 6 show the distribution of impurity concentrations along a depthdirection of an intermediate semiconductor region 24. FIG. 7 shows thedistribution of complex defects along a depth direction of theintermediate semiconductor region 24.

First, as shown in FIG. 1, a semiconductor stack is prepared, and thesemiconductor stack consists of n⁺ type cathode semiconductor region 22,n⁻ type (or i type) intermediate semiconductor region 24, and p⁺ typeanode semiconductor region 26, which are stacked together. Thesemiconductor stack is made from silicon wafers. The cathodesemiconductor region 22 is formed by injecting phosphorus ions into thebottom surface of an n⁻ type silicon wafer, followed by thermaldiffusion. The anode semiconductor region 26 is formed by injectingboron ions into the top surface of an n⁻ type silicon wafer, followed bythermal diffusion. The same thermal diffusion process can be performedto form both the cathode semiconductor region 22 and the anodesemiconductor region 26.

Impurities from the ingot stage are present in the semiconductor stack.One of these impurities is carbon. In the present embodiment, theconcentration of carbon intrinsically contained within the intermediatesemiconductor region 24 is approximately 2×10¹⁴ cm⁻³. The concentrationof carbon can be determined by, for example, converting from theabsorbency of infrared absorption measurements. The concentration ofintrinsically contained carbon is approximately uniform along the depthdirection of the intermediate semiconductor region 24. FIG. 5 shows thedistribution of the carbon concentration of the intermediatesemiconductor regions 24 in the depth direction. In FIG. 5, the carbonconcentrations of the intermediate semiconductor regions 24 obtainedfrom different silicon wafers are shown by 12 a and 14 a. The carbonconcentration originally contained differs for each silicon wafer.

Next, as shown in FIG. 2, carbon ions are injected toward theintermediate semiconductor region 24 from the anode semiconductor region26 side. It is preferred that the depth at which the carbon ions areinjected is set to be in the vicinity of the boundary between the anodesemiconductor region 26 and the intermediate semiconductor region 24. Itis even more preferred that the depth at which the carbon ions areinjected is eccentrically located slightly more towards the intermediatesemiconductor region 24 than at the above-mentioned boundary. After thecarbon ions are injected, it is preferred that the semiconductor regionis heated with a heating process set between 800 degrees Celsius and1300 degrees Celsius. By performing this heating process, the damageincurred by the anode semiconductor region 26 and the intermediatesemiconductor region 24 when the carbon ions were injected can berecovered. Further, by performing the heating process, the introducedcarbon ions can be displaced in the lattice location of the intermediatesemiconductor region 24, and substitutional carbon 42 is consequentlyformed. If the beating process is below 800 degrees Celsius, theefficiency in forming substitutional carbon 42 decreases. Further, aheating process of above 1300 degrees Celsius is undesirable because thesilicon would melt. It is therefore preferred that the heating processis set to be between 800 degrees Celsius and 1300 degrees Celsius. Whenthese steps are performed, the maximum concentration of substitutionalcarbon 42 in the local region of the intermediate semiconductor region24 is adjusted to approximately 1×10¹⁵ cm⁻³.

FIG. 6 shows the distribution of carbon concentration in the depthdirection of the intermediate semiconductor regions 24 after the carbonions have been injected. Broken line 42 in FIG. 6 shows theconcentration distribution of substitutional carbon 42 which has beenintroduced to the intermediate semiconductor region 24. 12 a of FIG. 6shows the concentration distribution of carbon included in theintermediate semiconductor region 24 of 12 a of FIG. 5 aftersubstitutional carbon 42 has been introduced. 14 a of FIG. 6 shows theconcentration distribution of carbon included in intermediatesemiconductor region 24 of 14 a of FIG. 5 after substitutional carbon 42has been introduced. As shown in FIG. 6, substitutional carbon 42 whichwas introduced is much greater in quantity than the quantity of carbonintrinsically contained in the intermediate semiconductor region 24. Asa result, after the substitutional carbon 42 has been introduced, thedifference between carbon concentrations 12 a and 14 a at the injecteddepth (the intermediate semiconductor regions 24) becomes relativelysmaller. In FIGS. 5 and 6, the concentration shown on the horizontalaxis has a logarithmic scale. That is, the difference between carbonconcentrations 12 a and 14 a of the intermediate semiconductor regions24 obtained from different silicon wafers becomes substantiallynegligible.

The depth at which the carbon is injected and the carbon concentrationbecomes maximum can easily be controlled by adjusting the half width ofthe injected energy (FWHM1) and the quantity of the dose (Dose1). In thecase of light ions such as carbon, the depth at which the carbon isinjected and the carbon concentration becomes maximum can be controlledwithin a range of several sum from the top surface of the semiconductorstack. The maximum carbon concentration can be estimated from the halfwidth of the injected energy (FWHM1) and the quantity of the dose(Dose1), and can be represented as Dose1/FWHM1.

Next, as shown in FIG. 3, anode electrode 32 is formed at the topsurface of anode semiconductor region 26. After anode electrode 32 isformed, helium ions are irradiated toward the intermediate semiconductorregion 24 from the cathode semiconductor region 22 side. Point defects44 are formed in the intermediate semiconductor region 24 which has beenirradiated with the helium ions. The helium ions are irradiated from thecathode semiconductor region 22 side in order to prevent charge-updamage to an oxide film formed at the anode side. However, helium ionsmay also be irradiated from the anode side as necessary. At thisjuncture, the depth of the intermediate semiconductor region 24 at whichthe maximum quantity of point defects 44 is to be formed is adjusted toapproximately conform to the position at which the maximum concentrationof the substitutional carbon 42 is introduced. In other words, theregion in the intermediate semiconductor region 24 at which the maximumconcentration of substitutional carbon 42 is introduced hasapproximately the same depth as the region in the intermediatesemiconductor region 24 where the maximum quantity of point defects 44is formed. The depth of the intermediate semiconductor region 24 wherethe maximum quantity of point defects 44 is formed conformsapproximately to the depth at which the maximum concentration of heliumions is introduced. As a result, the depth of the intermediatesemiconductor region 24 at which the maximum quantity of point defects44 are formed can easily be controlled by adjusting the half width ofthe irradiation energy of the helium ions (FWHM2) and the quantity ofthe dose (Dose2). The maximum introduced concentration of helium ionscan be estimated from the half width of the irradiation energy (FWHM2)and the quantity of the dose (Dose2), and can be represented asDose2/FWHM2. The maximum concentration of helium ions is approximately5×10¹⁵ cm⁻³.

Next, as shown in FIG. 4, a heating process is performed in the rangebetween 200 degrees Celsius and 600 degrees Celsius. By performing thisheating process, the carbon contained in the intermediate semiconductorregion 24 (including both the intrinsically contained carbon andsubstitutional carbon 42 which was previously introduced) and pointdefects 44 are combined to form complex defects 46. If the heatingprocess is below 200 degrees Celsius, the efficiency in forming complexdefects 46 decreases. A heating process above 600 degrees Celsius isundesirable because the defects may be diffused or destroyed. It istherefore preferred that the heating process is performed at atemperature between 200 degrees Celsius and 600 degrees Celsius.

As shown in FIG. 7, point defects 44 are formed in a quantity that isgreater than the carbon concentration of the intermediate semiconductorregion 24. When a large quantity of point defects 44 are formed,quantities of complex defects 12 b and 14 b are determined based oncarbon concentrations 12 a and 14 a of intermediate semiconductor region24. As a result, the difference between quantities of complex defects 12b and 14 b become substantially negligible because the differencebetween carbon concentrations 12 a and 14 a is negligible. There isconsequently no variation in the characteristics of the semiconductordevices that are obtained. The yield of semiconductor devices can thusbe increased by utilizing the aforementioned manufacturing method.

Explaining the step for forming complex defects 46 in more detail, thefollowing phenomenon occurs. When the helium ions are irradiated intothe intermediate semiconductor region 24, substitutional silicon isejected, thus forming vacancies (V: an example of a point defect) andinterstitial silicon (I: an example of a point defect). Vacancies (V)and interstitial silicon (I) are thermally unstable. As a result,vacancies (V) and interstitial silicon (I) are thermally stabilized bybeing combined with surrounding impurities (oxygen or carbon). Forexample, vacancies (V) and oxygen combine to form complex defects (tofunction as an electron trap) that have an energy level of approximately0.19 eV below the conduction band. Further, interstitial carbon (Ci) isformed by replacing substitutional carbon 42 with interstitial silicon(I). Interstitial carbon (Ci) and oxygen combine to form complex defects(to function as a positive hole trap) that have an energy level ofapproximately 0.35 eV above the valence band.

In the above embodiment, by introducing a large quantity of the carbonions, the concentration of carbon (including both the concentration ofcarbon intrinsically contained and the concentration of substitutionalcarbon 42 which was intentionally introduced) in intermediatesemiconductor regions 24 obtained from different silicon wafers can beuniformized. Therefore, complex defects 46 which function as positivehole taps in intermediate semiconductor regions 24 obtained fromdifferent silicon wafers can also be uniformized. The lifetime of PINtype diode 10 can be controlled by forming complex defects 46 inintermediate semiconductor regions 24, and PIN type diode 10 can berealized with reduced loss, reduced recovery surge voltage, etc. Byusing the manufacturing method of the present embodiment, PIN typediodes 10 which have equivalent switching characteristics can beobtained in a stable manner even when a plurality of PIN type diodes 10are manufactured.

Moreover, if required, complex defects that function as electron trapscan be made uniform, by means of injecting a large quantity of oxygen inintermediate semiconductor regions 24 obtained from different siliconwafers. In this case, similarly, the switching characteristics can beimproved.

The following variants can be adopted in the aforementionedmanufacturing method.

(1) In the method of forming point defects, electron beam irradiation, γbeam irradiation, neutrons, etc. may be utilized instead of helium ionirradiation.

(2) The step of ion-injection of impurities (carbon in the exampleabove), may be performed after the point defects have been formed.Alternatively, this step may be performed simultaneously with the stepof forming the point defects.

(3) A PIN type diode was used in the aforementioned example. However, anIGBT (Insulated Gate Bipolar Transistor), MOSFET (Metal OxideSemiconductor Field Effect Transistor), Bipolar Transistor, thyristor,etc. may equally well be utilized.

Second Embodiment

Shown in FIG. 8(A) is a simplified cross-sectional diagram of essentialparts of semiconductor device 100. The semiconductor device 100 is atype of non-punch-through IGBT (Insulated Gate Bipolar Transistor)semiconductor device. FIG. 8(A) shows the unit structure of thesemiconductor 100. The semiconductor 100 is made from silicon wafers.

The semiconductor 100 comprises a collector electrode 152, which is astacked layer formed by stacking aluminum, titanium, and nickel.

A collector semiconductor region 154 which includes p⁺ type impurities(typically boron) is formed above the collector electrode 152. Theconcentration of impurities in the collector semiconductor region 154 isadjusted to be approximately 1×10¹⁸ cm⁻³.

A n-type base semiconductor region 156 which includes n-type impurities(typically phosphorus) is formed above the collector semiconductorregion 154. The concentration of impurities in the n-type basesemiconductor region 156 is adjusted to be approximately 7×10¹³ cm⁻³.

A p-type base semiconductor region 162 which includes p-type impurities(typically boron) is formed above the n-type base semiconductor region156. The p-type base semiconductor region 162 is separated from thecollector semiconductor region 154 by the n-type base semiconductorregion 156. The concentration of impurities in the p-type basesemiconductor region 162 is adjusted to be approximately 1×10¹⁷ to5×10¹⁷ cm⁻³.

An emitter semiconductor region 166 which includes n-type impurities(typically phosphorus) is selectively formed above the p-type basesemiconductor region 162. The emitter semiconductor region 166 isseparated from the n-type base semiconductor region 156 by the p-typebase semiconductor region 162. The concentration of impurities in theemitter semiconductor region 166 is adjusted to be approximately 1×10¹⁹to 1×10²⁰ cm⁻³.

A base contact semiconductor region 164 which includes p-type impurities(typically boron) is selectively formed above the p-type basesemiconductor region 162. The concentration of impurities in the basecontact semiconductor region 164 is adjusted to be approximately 1×10¹⁹to 1×10²⁰ cm⁻³.

A trench gate electrode 174 faces, via a gate insulating film 172, theportion of the p-type base semiconductor region 162 that separates theemitter semiconductor region 166 and the n-type base semiconductorregion 156. The gate insulating film 172 is made of oxide silicon. Thetrench gate electrode 174 is made of polysilicon.

An emitter electrode 168 made of aluminum is formed above the emittersemiconductor region 166 and the base contact semiconductor region 164.The emitter electrode 168 is connected to the emitter semiconductorregion 166 and the base contact semiconductor region 164. The emitterelectrode 168 and the trench gate electrode 174 are electricallyisolated from one another.

In the semiconductor device 100, the complex defects 146 which wereformed by the combining of carbon (including both the intrinsicallycontained carbon and the substitutional carbon 142 introducedafterwards) and the point defects 144 are formed in the vicinity of theboundary between the collector semiconductor region 154 and the n-typebase semiconductor region 156. FIG. 8(B) shows the concentrationdistribution of carbon and concentration distribution of the complexdefects 146 along the direction that joins the collector semiconductorregion 154 and the emitter semiconductor region 166. Broken line 181represents the concentration distribution of carbon intrinsicallycontained in a silicon wafer. Solid line 182 represents theconcentration distribution of the substitutional carbon 142 which wasintroduced later on. Broken line 183 represents the concentrationdistribution of the complex defects 146. The depth where theconcentration of the substitutional carbon 142 is highest and the depthat which the largest quantity of the complex defects 146 are formed areboth locally located in the vicinity of the boundary between thecollector semiconductor region 154 and the n-type base semiconductorregion 156. The complex defects 146 provide locations where electronsand positive holes recombine, thereby improving reverse-recoverycharacteristics.

The semiconductor 100 is manufactured according to the followingprocedure.

First, a silicon wafer having a phosphorus concentration of 7×10¹³ cm⁻³is prepared. A CZ substrate which has been formed by the Czochralakimethod can be utilized for this silicon wafer. Next, using ioninjection, the p-type base semiconductor region 162 is formed byinjecting boron from the top surface of the silicon wafer. Further,using ion injection, the emitter semiconductor region 166 is formed byinjecting phosphorus from the top surface of the p-type basesemiconductor region 162. Further, using ion injection, the base contactsemiconductor region 164 is selectively formed by selectively injectingboron from the top surface of the p-type base semiconductor region 162.Next, a trench that penetrates p-type base semiconductor region 162 isformed from the top surface of the silicon wafer by means of etching.The side walls of the trench are coated with the gate insulating film172. Then, the trench electrode 174 is filled into the trench, which hasbeen coated with the gate insulating film 172. Next, the emitterelectrode 168, which is connected to the emitter semiconductor region166 and the base contact semiconductor region 164, is formed.

Next, using high-energy ion injection, the substitutional carbon 142 isintroduced at a predetermined depth of the silicon wafer by injectingcarbon ions from the bottom surface of the silicon wafer. The depth atwhich the substitutional carbon 142 is introduced is set to be in thevicinity of the boundary between the collector semiconductor region 154(to be formed later) and the n-type base semiconductor region 156. It ispreferred that the depth at which the substitutional carbon 142 isinjected is eccentrically located slightly more towards the intermediatesemiconductor region 24 than at the above-mentioned boundary. Theconcentration of the substitutional carbon 142 is set to be higher thanthe concentration of carbon intrinsically contained in the siliconwafer.

Next, using ion injection, boron is injected from the bottom surface ofthe silicon wafer. The region where the boron is introduced correspondsto an area of the collector semiconductor region 154. Next, a heatingprocess is implemented at or below 600 degrees Celsius and theintroduced boron is activated to form the collector semiconductor region154. The complex defects 146 are simultaneously formed with this heatingprocess. The point defects 144 were simultaneously formed when the stepof injecting carbon ions and the step of injecting boron wereimplemented. Therefore, by this heating process, the substitutionalcarbon 142 and the point defects 144 combine to form the complex defects146.

Next, the collector electrode 152 is deposited on the bottom surface ofthe silicon wafer. Through these steps, the semiconductor device 100 canbe manufactured.

In this second embodiment, by introducing a large quantity of carbon,the variation in the concentration of carbon in different silicon wafersbecomes negligible. Accordingly, the complex defects 146, which functionas positive hole traps, are formed uniformly among the different siliconwafers. Once the complex defects 146 are formed in the vicinity of theboundary between the collector semiconductor region 154 and the n-typebase semiconductor region 156, it becomes possible to control thelifetime of carriers, and the semiconductor 100 can be realized withreduced loss, reduced recovery surge voltage, etc. Even if a pluralityof the semiconductor devices 100 are manufactured, the plurality of thesemiconductor devices 100, which all have similar switchingcharacteristics, can be stably obtained by utilizing the manufacturingmethod of the present embodiment.

When a large quantity of oxygen is injected, if the need arises, complexdefects which function as electron traps can be uniformly formed amongdifferent silicon wafers. In this case, switching characteristics can besimilarly improved.

Third Embodiment

Shown in FIG. 9(A) is a simplified cross-sectional diagram of essentialparts of the semiconductor device 102. The semiconductor device 102 is atype of punch-through IGBT (Insulated Gate Bipolar Transistor)semiconductor device. FIG. 9(A) shows the unit structure of thesemiconductor device 102. The semiconductor device 102 is made fromsilicon wafers. Component parts of the semiconductor device 102 that arepractically the same as in the semiconductor device 100 of FIG. 8(A)will be represented with the same numerals, and descriptions thereofwill be omitted.

The semiconductor device 102 comprises a buffer semiconductor region155, which includes n-type impurities phosphorus). The buffersemiconductor region 155 is disposed between a collector semiconductorregion 153 and the n-type base semiconductor region 156. Further, thesemiconductor device 102 is characterized in that thickness thereof isrelatively thick. The concentration of impurities of a buffersemiconductor region 155 is adjusted to be approximately above 1×10¹⁷cm⁻³. The concentration of impurities of the collector semiconductorregion 153 is adjusted to be 1×10¹⁸ cm⁻³.

In the semiconductor device 102, the complex defects 146 which wereformed by the combining of oxygen (including both the intrinsicallycontained oxygen and the introduction oxygen 143 introduced afterwards)and point defects 144 are formed in the vicinity of the boundary betweenthe collector semiconductor region 154 and the n-type base semiconductorregion 156. FIG. 9(B) shows the concentration distribution of oxygen andconcentration distribution of the complex defects 146 along thedirection that joins the collector semiconductor region 153 and theemitter semiconductor region 166. Broken line 184 represents theconcentration distribution of oxygen intrinsically contained in asilicon wafer. Solid line 185 represents the concentration distributionof the introduction oxygen 143 which was introduced later on. Brokenline 186 represents the concentration distribution of the complexdefects 146. The depth where the concentration of the introductionoxygen 143 is highest and the depth at which the largest quantity of thecomplex defects 146 are formed are both locally located in the vicinityof the boundary between the collector semiconductor region 153 and thebuffer semiconductor region 156. The complex defects 146 providelocations where electrons and positive holes recombine, therebyimproving reverse-recovery characteristics.

The semiconductor 102 is manufactured according to the followingprocedure.

First, a silicon wafer having a boron concentration of 1×10¹⁸ cm⁻³ isprepared. This silicon wafer becomes the collector semiconductor region153. A CZ substrate which has been formed by the Czochralaki method canbe utilized for this silicon wafer. Then, by utilizing epitaxial growth,the buffer semiconductor region 155 is grown from the top surface of thesilicon wafer. Next, using ion injection, the introduction oxygen 143 isformed at a predetermined depth of the buffer semiconductor region 155by injecting oxygen ions from the top surface of the buffersemiconductor region 155. It is preferred that the depth at which theintroduction oxygen 143 is formed is set to be in the vicinity of theboundary between the collector semiconductor region 153 (to be formedlater) and the buffer semiconductor region 155. It is even morepreferred that the depth at which the introduction oxygen 143 is formedbe located slightly more towards the buffer semiconductor region 155side than at the above-mentioned boundary. The concentration of theintroduction oxygen 143 is set to be higher than the concentration ofoxygen intrinsically contained.

Next, utilizing epitaxial growth, the p-type base semiconductor region162 is grown from the top surface of the buffer semiconductor region155. Then, using ion injection, the emitter semiconductor region 166 isformed by selectively injecting phosphorus from the top surface of thep-type base semiconductor region 162. Further, using ion injection, thebase contact semiconductor region 164 is selectively formed byselectively injecting boron from the top surface of the p-type basesemiconductor region 162. Next, a trench that penetrates the retype basesemiconductor region 162 is formed from the top surface of the siliconwafer by means of etching. The side walls of the trench are coated withthe gate insulating film 172. Then, the trench electrode 174 is filledinto the trench, which has been coated with the gate insulating film172. Next, the emitter electrode 168, which is connected to the emittersemiconductor region 166 and the base contact semiconductor region 164,is formed.

Next, helium ions are irradiated from the bottom surface of the siliconwafer towards the vicinity of the boundary of the collectorsemiconductor region 153 and the buffer semiconductor region 155. Thepoint defects 144 are formed in the region where the helium ions wereirradiated. The depth at which the largest quantity of the point defects144 is formed is adjusted to conform approximately with to the positionwhere the maximum concentration of the introduction oxygen 143 isintroduced.

Next, a heating process is implemented at or below 600 degrees Celsius,where the oxygen (including both the intrinsically contained oxygen andthe introduction oxygen 143 introduced afterwards) and the point defects144 combine to form the complex defects 146.

Next, the collector electrode 152 is deposited on the bottom surface ofthe silicon wafer. By completing the aforementioned steps, thesemiconductor 102 can be manufactured.

In this third embodiment, by introducing a large quantity of oxygen, thevariation in the concentration of oxygen in different silicon wafersbecomes negligible. Accordingly, the complex defects 146, which functionas electron traps, are formed uniformly among the different siliconwafers. Once the complex defects 146 are formed in the vicinity of theboundary between the collector semiconductor region 153 and the basesemiconductor region 155, it becomes possible to control the lifetime ofcarriers, and the semiconductor device 102 can be realized with reducedloss, reduced recovery surge voltage, etc. Even if a plurality of thesemiconductor devices 102 are manufactured, the plurality of thesemiconductor devices 102, which all have similar switchingcharacteristics, can be stably obtained by utilizing the manufacturingmethod of the present embodiment.

When a large quantity of carbon is injected, if the need arises, complexdefects which function as positive hole traps can be uniformly formedamong different silicon wafer. In this case, switching characteristicscan be similarly improved.

Fourth Embodiment

Shown in FIG. 10(A) is a simplified cross-sectional diagram of essentialparts of a semiconductor device 104. The semiconductor device 104 is atype of collector-short IGBT (Insulated Gate Bipolar Transistor)semiconductor device. FIG. 10(A) shows the unit structure of thesemiconductor device 104. The semiconductor device 104 is made fromsilicon wafers. Component parts of the semiconductor device 104 that arepractically the same as in the semiconductor device 100 of FIG. 8(A)will be represented with the same numerals, and descriptions thereofwill be omitted.

In the semiconductor device 104, a plurality of collector semiconductorregions 157 is dispersively formed between the collector electrode 152and the n-type base semiconductor region 156. A collector-shortsemiconductor region 151, which include n-type impurities (phosphorus),is formed between the collector semiconductor regions 157. The thicknessof the collector semiconductor region 157 and the thickness of thecollector-short semiconductor region 151 are adjusted to beapproximately equal. The concentration of impurities in thecollector-short semiconductor region 151 is adjusted to be approximatelyabove 1×10¹⁹ cm⁻³. The collector electrode 152 and the n-type basesemiconductor region 156 are electrically connected via thecollector-short semiconductor region 151.

In semiconductor device 104, the complex defects 146 which were formedby the combining of nitrogen (including both the intrinsically containednitrogen and the introduction nitrogen 145 introduced afterwards) andpoint defects 144 are formed in the vicinity of the boundary between thecollector semiconductor region 157 and the n-type base semiconductorregion 156. FIG. 10(B) shows the concentration distribution of nitrogenand concentration distribution of the complex defects 146 along thedirection that joins the collector semiconductor region 154 and theemitter semiconductor region 166. Broken line 187 represents theconcentration distribution of nitrogen intrinsically contained in asilicon wafer. Solid line 188 represents the concentration distributionof the introduction nitrogen 145 which was introduced later on. Brokenline 189 represents the concentration distribution of the complexdefects 146. The depth where the concentration of the introductionnitrogen 145 is highest and the depth at which the largest quantity ofthe complex defects 146 are formed are both locally located in thevicinity of the boundary between the collector semiconductor region 157and the n-type base semiconductor region 156, and in the vicinity of theboundary between the collector-short semiconductor region 151 and then-type base semiconductor region 156. The complex defects 146 providelocations where electrons and positive holes recombine, therebyimproving reverse-recovery characteristics.

The semiconductor 104 is manufactured according to the followingprocedure.

First, a silicon wafer having a boron concentration of 7×10¹³ cm⁻³ isprepared. A CZ substrate which has been formed by the Czochralaki methodcan be utilized for this silicon wafer. Next, using ion injection, thep-type base semiconductor region 162 is formed by injecting boron fromthe top surface of the silicon wafer. Further, using ion injection, theemitter semiconductor region 166 is formed by selectively injectingphosphorus from the top surface of the p-type base semiconductor region162. Further, using ion injection, the base contact semiconductor regionsemiconductor region 162. Next, a trench that penetrates the p-type basesemiconductor region 162 is formed from the top surface of the siliconwafer by means of etching. The side walls of the trench are coated withthe gate insulating film 172. Then, the trench electrode 174 is filledinto the trench, which has been coated with the gate insulating film172. Next, the emitter electrode 168, which is connected to the emittersemiconductor region 166 and the base contact semiconductor region 164,is formed.

Next, using high-energy ion injection, the introduction nitrogen 145 isformed at a predetermined depth of the silicon wafer by injectingnitrogen ions from the bottom surface of the silicon wafer. The depth atwhich the introduction nitrogen 145 is formed is set to be in thevicinity of the boundary between the collector semiconductor region 157(to be formed later) and the n-type base semiconductor region 156.Further, the depth at which the introduction nitrogen 145 is formed isset to be in the vicinity of the boundary between the collector-shortsemiconductor region 151 (to be formed later) and the n-type basesemiconductor region 156. It is further preferred that the depth atwhich the introduction nitrogen 145 is injected is eccentrically locatedslightly more towards the n-type base semiconductor region 156 than atthe two boundaries mentioned above. The concentration of theintroduction nitrogen 145 is set to be higher than the concentration ofcarbon intrinsically contained in the silicon wafer.

Next, using ion injection, boron is selectively injected from the bottomsurface of the silicon wafer. The region where the boron is introducedcorresponds to an area of the collector semiconductor region 157. Usingion injection, phosphorus is selectively injected from the bottomsurface of the silicon wafer. The region where the phosphorus isintroduced corresponds to an area of the collector-short semiconductorregion 151. Next, a laser-annealing method is utilized to activate theintroduced boron and phosphorus, and to form the collector semiconductorregion 157 and the collector-short semiconductor region 151. Then, aheating process is implemented at or below 600 degrees Celsius to formthe complex defects 146. When the step of injecting nitrogen ions, thestep of injecting boron, the step of injecting phosphorus, and the stepof the laser-anneal were implemented, the point defects 142 weresimultaneously formed. Due to this heating process, the point defects144 and nitrogen (including both the intrinsically contained nitrogenand the introduction nitrogen 145 which was introduced later on) arecombined, and the complex defects 146 are formed.

Next, the collector electrode 152 is deposited on the bottom surface ofthe silicon wafer. Through these steps, the semiconductor device 104 canbe manufactured.

In this fourth embodiment, by introducing a large quantity of nitrogen,the variation in the concentration of nitrogen in different siliconwafers becomes negligible. Accordingly, the complex defects 146, whichfunction as electron traps, are formed uniformly among the differentsilicon wafers. Once the complex defects 146 are formed in the vicinityof the boundary between the collector semiconductor region 157 and then-type base semiconductor region 156, it becomes possible to control thelifetime of carriers, and the semiconductor 104 can be realized withreduced loss, reduced recovery surge voltage, etc. Even if a pluralityof the semiconductor devices 104 are manufactured, the plurality of thesemiconductor devices 104, which all have similar switchingcharacteristics, can be stably obtained by utilizing the manufacturingmethod of the present embodiment.

When a large quantity of carbon is injected, if the need arises, complexdefects which function as positive hole traps can be uniformly formedamong different silicon wafers. In this case, switching characteristicscan be similarly improved.

Specific examples of the present invention are described above indetail, but these examples are merely illustrative and place nolimitation on the scope of the patent claims. The technology describedin the patent claims also encompasses various changes and modificationsto the specific examples described above.

Furthermore, the technical elements explained in the presentspecification and drawings provide technical value and utility eitherindependently or through various combinations. The present invention isnot limited to the combinations described at the time the claims arefiled. Further, the purpose of the example illustrated by the presentspecification and drawings is to satisfy multiple objectivessimultaneously, and satisfying any one of those objectives givestechnical value and utility to the present invention.

1. A semiconductor device comprising: a post-heated semiconductor regionhaving complex defects, wherein impurities of a non-conductive typecontained in the semiconductor region have an uneven concentrationdistribution along a depth direction of the semiconductor region.
 2. Thesemiconductor device according to claim 1, wherein the impurities of thenon-conduct type have a maximum concentration of greater than or equalto twice the minimum concentration along the depth direction of thepost-heated semiconductor region.
 3. A semiconductor device comprising:an anode semiconductor region that includes impurities of a firstconductivity type; a cathode semiconductor region that includes a highconcentration of impurities of a second conductivity type; and anintermediate semiconductor region that either includes a smallconcentration of impurities of the second type or substantially does notinclude impurities, wherein the intermediate semiconductor region isformed between the anode semiconductor region and the cathodesemiconductor region, wherein non-conductive impurities having an unevenconcentration distribution along the direction that joins the anodesemiconductor region and the cathode semiconductor region is included atleast in the intermediate region.
 4. The semiconductor device accordingto claim 3, wherein a position of the highest concentration of thenon-conductive impurities is located in the vicinity of a boundarybetween the anode semiconductor region and the intermediatesemiconductor region.
 5. The semiconductor device according to claim 3,wherein the non-conductive impurities have a maximum concentration thatis greater than or equal to twice the minimum concentration along thedirection that joins the anode semiconductor region and the cathodesemiconductor region.
 6. A semiconductor device comprising: a collectorelectrode; a collector semiconductor region that includes impurities ofa first conductivity type, wherein the collector semiconductor region isformed above the collector electrode; a second conductivity type basesemiconductor region that includes impurities of a second conductivitytype, wherein the second conductivity type base semiconductor region isformed above the collector semiconductor region; a first conductivitytype base semiconductor region that includes impurities of the firstconductivity type, wherein the first conductivity type basesemiconductor region is separated from the collector semiconductorregion by the second conductivity type base semiconductor region; anemitter semiconductor region that includes impurities of the secondconductivity type, wherein the emitter semiconductor region is separatedfrom the second conductivity type base semiconductor region by the firstconductivity type base semiconductor region; and a gate electrode thatfaces, via an insulating film, the first conductivity type basesemiconductor region that separates the second conductivity type basesemiconductor region and the emitter semiconductor region, whereinnon-conductive impurities having an unequal concentration distributionalong the direction that joins the collector semiconductor region andthe emitter semiconductor region are included at least in secondconductivity type base semiconductor region.
 7. The semiconductor deviceaccording to claim 6, wherein a position of the highest concentration ofthe non-conductive impurities is located in the vicinity of a boundarybetween the collector semiconductor region and the second conductivitytype base semiconductor region.
 8. The semiconductor device according toclaim 6, further comprising: a buffer semiconductor region that includesa higher concentration of impurities of the second conductivity typethan the second conductivity type base semiconductor region, wherein thebuffer semiconductor region is formed between the collectorsemiconductor region and the second conductivity type base semiconductorregion.
 9. The semiconductor device according to claim 8, wherein aposition of the highest concentration of the non-conductive impuritiesis located in the vicinity of a boundary between the collectorsemiconductor region and the buffer semiconductor region.
 10. Thesemiconductor device according to claim 7, wherein a plurality of thecollector semiconductor regions is intermittently above the collectorelectrode, and the collector electrode and the second conductivity typebase semiconductor region are electrically connected via spaces betweenneighboring collector semiconductor regions.
 11. The semiconductordevice according to claim 10, wherein a position of the highestconcentration of the non-conductive impurities is located in thevicinity of a boundary between the collector semiconductor region andthe second conductivity type base semiconductor region.
 12. Thesemiconductor device of according to claims 6, wherein thenon-conductive impurities have a maximum concentration of greater thanor equal to twice the minimum concentration along the direction thatjoins the collector semiconductor region and the emitter semiconductorregion.